The present invention relates to a method of producing a poly-V pulley which is used together with a V belt for transmitting rotational power.
As a poly-V pulley of this kind, for the purpose of insertion and coupling onto a shaft via a one-way clutch or a bearing, known is a poly-V pulley of a structure in which a cylindrical trunk is formed, an ear for preventing a V belt from disengaging is formed in each of the axial ends of the outer peripheral face of the trunk, and poly-V grooves are formed between the ears.
A method of producing such a poly-V pulley is disclosed in, for example, Japanese Laid Open Patent Publication No. 8-300082. The disclosed poly-V pulley is produced approximately in the following pressing steps. First, a disk-shaped blank configured by a rolled steel plate is drawn to form a first shaped member of a bottomed cup-like shape. Then, the bottom wall portion of the first shaped member is punched out to form a second shaped member of a bottomless cup-like shape. Thereafter, the second shaped member of a bottomless cup-like shape is shaped into a cylindrical trunk, and a preliminary ear is formed by a pressing work in each of the axial ends of the outer peripheral face of the trunk. Finally, the preliminary ears in the ends of the trunk are shaped into ears of a predetermined shape, and poly-V grooves are formed by a rolling work in the outer peripheral face of the trunk between the ears.
However, a sheet metal made poly-V pulley which is produced from a rolled steel plate by steps all of which are pressing steps requires a large number of steps and a long working time period, and its cost is high. In order to obtain a cylindrical trunk from a shaped member of a bottomed cup-like shape, particularly, the bottom wall portion of the shaped member of a bottomed cup-like shape must be punched out. The bottom wall portion becomes scrap or causes a material loss, and hence is uneconomical. In order to form ears so as to project in a necessary and sufficient manner, a thick blank is necessary. However, it is not easy to draw a thick blank into a bottomed cup-like shape.
It is an object of the invention to provide a method of producing a poly-V pulley which can easily produce a poly-V pulley configured by such a cylindrical trunk by a small number of steps, without producing a material loss, and at a low cost.
A first method of producing a poly-V pulley of the present invention is a method of producing a poly-V pulley which has a cylindrical trunk, first and second ears for preventing a V belt from disengagement from the trunk, the ears being projectingly formed respectively in axial ends of an outer peripheral face of the trunk, and poly-V grooves formed between the first and second ears on the outer peripheral face of the trunk, wherein the method comprises: a first step of cutting a thick pipe blank into a fixed dimension to obtain the trunk; a second step of projectingly forming first and second preliminary ears in axial ends of the outer peripheral face of the trunk by a pressing work in which axial end faces of the trunk are clamped between upper and lower dies each having an annular wedge-like projection, and the wedge-like projections are caused to bite the axial end faces of the trunk; and a third step of, by a rolling work, shaping the first and second preliminary ears into the first and second ears of a predetermined shape, and forming the poly-V grooves between the first and second ears.
According to the production method, since the trunk is obtained by cutting a thick pipe blank into a fixed dimension, a poly-V pulley of a predetermined shape can be easily obtained by only the two steps, ie., the single pressing step and the rolling step. Furthermore, the problem in the above-described pressing work in the conventional art is eliminated, whereby a material loss is produced by punching out a bottom wall portion of a shaped member of a bottomed cup-like shape.
A variant of the method of producing a poly-V pulley of the present invention is a method of producing a poly-V pulley which has a cylindrical trunk, first and second ears for preventing a V belt from disengagement from the trunk, the ears being projectingly formed respectively in axial ends of an outer peripheral face of the trunk, and poly-V grooves formed between the first and second ears on the outer peripheral face of the trunk, wherein the variant comprises: a first step of cutting a thick pipe blank into a fixed dimension to obtain the trunk; a second step of forming a V-shaped slot over a circumferential direction in an intermediate portion in a thickness direction of each of the axial end faces of the trunk, and projectingly forming first and second preliminary ears in axial ends of the outer peripheral face of the trunk by a first pressing work in which the axial end faces of the trunk are clamped between upper and lower dies each having an annular wedge-like projection, and the wedge-like projections are caused to bite the axial end faces of the trunk; a third step of forming an annular boss portion in a radially inner side with respect to the V-shaped slot of at least one of the axial end faces of the trunk making the V-shaped slot disappear, and increasing a projecting amount of the first preliminary ear or the second preliminary ear in the place by a second pressing work in which annular split pieces of the axial end faces of the trunk and outside the respective V-shaped slots are clamped between the upper and lower dies, thereby inwardly compressing in the axial direction by a depth of the V-shaped slot; and a fourth step of, by a rolling work, shaping the first and second preliminary ears into the first and second ears of a predetermined shape, and forming the poly-V grooves between the first and second ears.
According to the production method, since the trunk is obtained by cutting a thick pipe blank into a fixed dimension in the same manner as the first variant of the present invention, a cylindrical poly-V pulley which has an annular boss portion in at least one end can be easily obtained by the three steps, i.e., the two pressing steps and the rolling step. Furthermore, also the problem in that, as in the above-described pressing work in the conventional art, a material loss is eliminated.